Circuits for power-factor correction are also referred to as charge pumps or pump circuits. They are used, for example, to satisfy IEC Standard 1000-3-2, in which the electricity supply organizations have defined the acceptable mains current harmonics. It is therefore undesirable to draw high-frequency energy from the power supply network. The mains current which is drawn from the mains is, optimally, proportional to the mains voltage. Proportionality between the mains current and the mains voltage allows the maximum power transfer for any given cable size. Reactive currents which would occur if the mains voltage and the mains current were not proportional would cause cable losses, which place additional loads on the cables and thus leading to interference with other loads.
Such circuits for power-factor correction are used, inter alia, for ballasts for operation of gas-discharge lamps.
The present invention is based on a prior art as is known, for example, from EP-A-0 253 224, DE-A-38 41 227 or U.S. Pat. No. 5,488,269. The prior art in these documents is illustrated in the outline circuit in FIG. 1. In this circuit, an AC voltage source 10, in general the mains voltage, is connected to the inputs 14 and 16 of a rectifier 18 which comprises the four diodes DG1, DG2, DG3 and DG4.
First of all, reference will be made to the circuit arrangement illustrated by solid lines: an energy storage apparatus 20 is connected on the one hand to the junction point between two diodes DP1, DP2 and on the other hand at the connection 28 to a high-frequency voltage source 22, that is to say an AC voltage source which, in operation, provides a signal at a considerably higher frequency than the AC voltage source 10. This AC voltage source 22 is part of the actuation and load circuit 24, as is intended to be expressed by the double arrow 26. Arranged in parallel with the actuation and load circuit 24 is an energy storage capacitor CS, which is used to store the energy drawn from the AC voltage source 10 in order to supply the actuation and load circuit 24.
An alternative embodiment is shown by dashed lines in FIG. 1. This comprises an energy storage apparatus 20' which is connected on the one hand to the high-frequency voltage source 22 and on the other hand to the junction point between two diodes DP1', DP2'. The diodes DP2 and DP2' are used to prevent reactions from the actuation and load circuit 24 on the energy storage apparatus 20 or 20' respectively. The diodes, DP1, DP1', which are in the form of so-called "fast diodes" in comparison with the diodes DG1 to DG4 in the rectifier 18, are used to prevent energy from being pumped into the AC voltage source 10.
Taking account of the fact that such pump circuits are used, for example, in ballasts for operation of gas discharge lamps which are mass-produced items, the cost aspect is of major importance.